The operation of diesel and spark ignition internal combustion engines is typically accompanied by the formation of sludge, lacquer and resinous deposits which adhere to the moving engine parts and thereby reduce engine efficiency. In order to prevent or reduce the formation of these deposits, a wide variety of chemical additives have been developed for incorporation into lubricating oils. These additives are commonly referred to as detergents and dispersants. Dispersants have the ability to keep deposit forming materials suspended in the oil so as to retard deposit formation during engine operation. Detergents have the ability to remove preexisting deposits from the engine during engine operation and to neutralize acids in railroad, marine and automotive engines.
Among the many additives which have been developed for this purpose, Group II metal overbased sulfurized alkylphenol compositions have been found to be highly effective detergent/dispersants for use in lubricating oils. Furthermore, these additives are excellent oxidation and corrosion inhibitors and, by virtue of their alkalinity reserve, have the ability to neutralize acidic combustion and oxidation products. Such acidic products form during engine operation, particularly when operated on high sulfur containing fuels, and tend to accumulate in the lubricating oil. The sulfur in these compositions has antioxidant activity.
The ability of Group II metal overbased sulfurized alkylphenol compositions to neutralize such acidic products can be directly measured by determining the total base number (TBN) of the composition. Higher TBNs reflect a greater capacity for these compositions to neutralize acids generated during engine operation. The term “overbased” is used to describe those sulfurized alkaline earth metal alkylphenates in which the ratio of the number of equivalents of the alkaline earth metal moiety to the number of equivalents of the phenol moiety is greater than one, and is usually greater than 1.2 and may be as high as 4.5 or greater. In contrast, the equivalent ratio of alkaline earth metal moiety to phenol moiety in “neutral” alkaline earth metal sulfurized alkylphenol is 1. Thus, the “overbased” material typically contains greater than 20% in excess of the alkaline earth metal present in the corresponding “neutral” material. For this reason, “overbased” alkaline earth metal sulfurized alkylphenol has a greater capability for neutralizing acidic matter than does the corresponding “neutral” alkaline earth metal sulfurized alkylphenol.
The preparation of Group II metal overbased sulfurized alkylphenate compositions is well known in the art. A number of patents have discussed processes in which overbasing is accomplished by the direct addition of ethylene glycol and carbon dioxide.
For example, U.S. Pat. No. 3,178,368 discloses the basic process for making metal overbased alkylphenates using an alkylphenol, a sulfonate, a high molecular weight alcohol, lubricating oil, sulfur, hydrated lime (or calcium oxide), ethylene glycol and carbon dioxide. The metal overbased sulfurized alkylphenates prepared by this process have greater than 20% metal compared to the neutral alkylphenates.
U.S. Pat. No. 3,367,867 discloses the preparation of low-foaming metal overbased alkylphenates by starting with alkylphenols wherein the alkyl group is a mixture of straight and branched chain alkyl groups.
U.S. Pat. No. 3,801,507 discloses sulfurized metal alkylphenates that have a ratio of sulfur to calcium between 1 and 2 which provides for better dispersancy and improved antioxidant activity.
U.S. Pat. No. 4,251,379 discloses a process for increasing the TBN of metal overbased sulfurized alkylphenates to more than 250.
U.S. Pat. No. 4,744,921 discloses the use of a sulfurization catalyst in the preparation of metal overbased sulfurized alkylphenates to obtain products having a lower crude sediment and TBN greater than 300.
U.S. Pat. No. 5,320,762 discloses the use of alkylphenols having a substantially straight chain alkyl substituent attached to the phenol ring in a middle position to obtain metal overbased sulfurized alkylphenates which possess low viscosity at high TBNs.
U.S. Pat. Nos. 5,714,443 and 5,716,914 disclose the preparation and use of metal overbased sulfurized alkylphenates modified by incorporation of a mono-carboxylic acid or a di- or polycarboxylic acid in lubricating oils. Also disclosed is the use of a metal halide catalyst to increase the TBN in the metal overbased sulfurized alkylphenate product.
European Patent No. 259974 discloses a process for the preparation of Group II overbased sulfurized alkylphenols characterized as possessing a TBN of 300 or greater and having viscosities less than 1000 cSt at 100° C. In particular. This patent teaches that the hydrolytic stability of the overbased sulfurized alkylphenols is improved by the use of a sulfurization catalyst, such as 2-mercaptobenzothiozole and derivatives thereof.
European Patent No. 989178 discloses a process for the preparation of an overbased alkaline earth metal phenate sulfide having a high base number and good hydrolytic stability.
U.S. Pat. No. 4,465,603 discloses the replacement of the ethylene glycol employed in the overbasing step in the preparation of metal overbased sulfurized alkylphenates with dimethyl carbonate. It is believed that the hydrolysis products of dimethyl carbonate are likely carbon dioxide and methyl alcohol.
Typically, Group II metal overbased sulfurized alkylphenol compositions are prepared by treating alkylphenol in a suitable diluent (e.g., a lubricating oil) with an amount of an alkaline earth metal hydroxide, oxide and/or alkoxide in excess of that necessary to neutralize the phenol and then sulfurizing the resulting product, optionally in the presence of a sulfurizing catalyst. The sulfurized product is then treated with carbon dioxide to provide the Group II metal overbased sulfurized alkylphenol composition.
Such Group II metal overbased sulfurized alkylphenols are useful for preparing additive compositions which are further used to prepare a fully formulated lubricant composition suitable for use in an internal combustion engine. Typically, the additive composition is prepared as a concentrate and is then shipped to a point where it is used to prepare fully formulated lubricant compositions by combining requisite amounts of several additive compositions, including a Group II metal overbased sulfurized alkylphenol composition, to a base stock.
In order to reduce shipping costs, the Group II metal overbased sulfurized alkylphenol is preferably prepared to contain as little diluent as possible. Additionally, in order to achieve the maximum amount of acid neutralization possible, the Group II metal overbased sulfurized alkylphenol is preferably prepared to contain as high a TBN as possible.
Thus, while Group II metal overbased sulfurized alkylphenols produced in the prior art are reported to possess TBNs of up to about 350 or more, in practice, commercial Group II metal overbased sulfurized alkylphenols typically have a TBN of less than about 300, and more typically less than about 275, so as to ensure that the composition possesses acceptable viscosity because viscosity typically increases with an increase in the TBN. In view of the above, it is generally desirable to increase the TBN of the Group II metal overbased sulfurized alkylphenols.
The chemistry in the conventional preparation of overbased sulfurized alkylphenols begins with the reaction of lime (calcium hydroxide) and the alkylphenol to form calcium phenate with the aid of ethylene glycol as a promoter. This reaction typically begins at approximately 135° C., with the generation of water. The calcium phenate quickly reacts with sulfur in a reaction that cross-links the alkylphenol aromatic rings. At this point, the reaction is ready for carbonation.
The conventional carbonation process uses carbon dioxide and ethylene glycol for the preparation of overbased sulfurized alkylphenols. The key change in the present process is the replacement of the carbon dioxide/ethylene glycol carbonation process with a simpler and faster ethylene carbonate process. Ethylene carbonate serves as a source of equal molar quantities of carbon dioxide and ethylene glycol through hydrolysis.
Optimization of processing properties for highly overbased sulfurized alkylphenols is highly empirical, owing to the high degree of overbasing which causes the overbased sulfurized phenol compositions to be less stable and, accordingly, more susceptible to degradation. Carbonation of sulfurized alkylphenols by the prior art process is the most time consuming processing step for production of overbased sulfurized alkylphenols. This is because gaseous carbon dioxide must be added carefully and slowly at the right temperature. For example, if carbon dioxide is charged too rapidly, a portion of the gas can simply escape through the reactor to the atmosphere or vent. In such a case, insufficient carbon dioxide will ultimately be delivered to the reactor resulting in high crude sediment. Fundamentally, this is an issue of mixing and reaction rate, because the gaseous carbon dioxide must be added to the reactor at temperatures far above the boiling point. A further complication may arise if the carbon dioxide is inadequately dispersed in the reaction mixture. This can occur if the reactor does not have sufficient agitation relative to the rate of gas introduction. Inadequate agitation can result in “local over-carbonation” which can result in poor product performance such as hydrolytic stability.
Overbased sulfurized alkylphenol carbonation is a complex process and is highly dependent on reaction conditions. The reactions involved are subtle and not perfectly understood. For example, glycol plays a critical role in this process and the overbased sulfurized alkylphenol undergoes oxidation with subsequent condensation of the reaction intermediates.
The use of ethylene carbonate in the carbonation process of the present invention is advantageous because it eliminates the problems of timing the addition of carbon dioxide, adequately dispersing it, and correctly charging the ethylene glycol. This is because the hydrolysis of ethylene carbonate to ethylene glycol and carbon dioxide occurs in situ which results in the carbon dioxide produced to be completely dispersed in the reaction medium.
It is believed that the present rapid carbonation process for overbasing sulfurized alkylphenols using ethylene carbonate instead of ethylene glycol and carbon dioxide can also be used for the preparation of highly overbased alkyl aromatic salicylic acid, sulfurized alkyl aromatic salicylic acid, and alkyl aromatic sulfonic acid and mixtures thereof with advantages similar to those observed for the preparation of overbased sulfurized alkyl phenol compositions.